I'm trying to find the most efficient way to upload some of my images to various forum threads from LR4. Right now, I use PS 5, File: Save for Web and Devices, which is cumbersome, as multiple tweaks seem to be necessary to find the right quality level to stay within the file size constraints. Ideally, I'd like to run some kind of script, but using the droplet function in Photoshop (File: Automate:create droplet) doesn't look like it will allow me to create the kind of custom action I have in mind for auto-resizing. Does anyone have any further thoughts or suggestions on what might be feasible?

You can create a publish to hard drive service in Lightroom and set the parameters you require in there (max height/width and file size among other things).Once it's done, you just drag the image you want to publish to the service you created and publish them. Lightroom will create files on your hard drive based on what you specified in the publish service settings. You can then upload those files where you need to.

You can also set up multiple publish via hard drive services to cater for differing requirments on forums/clubs, etc.

As an alternative, you can export with desired settings and name that set of settings. For example I have saved Nik1200 and Nik1000 settings to export to jpg, with the long side to 1200 or 1000 pixels, 300 kB max, sharpening to screen, and so on. On subsequent runs, I only select Nik1200 or Nik1000 settings. No need to adjust individual parameters.